Here is the explained tutorial for you,how to make USB bootable in windows 7.
Its very very useful to make bootable USB and Install Windows from it.It reduces the time of installation (In my case it was 40% faster than CD ROM).

1- Click on Start and Search CMD

2- Right click on CMD and choose Run as Administrator.

3- After that type “diskpart” (without the quotes)

4- DISKPART will be opened,Now type “list disk” it will display all drives attached to the PC.